Stable Isotope Abundance Patterns as Potential Biosignatures.

The abundance and distribution of stable isotopes of an element in a substance can provide insights regarding the source, synthesis, and environmental history of that substance. Because isotopic discrimination during chemical reactions can be unique to specific chemical pathways or environmental conditions, isotopic patterns within a substance or between related substances may provide insights into their formation. Biosynthetic pathways can create isotopic patterns that differ from patterns that arise from abiotic processes, but this is not universally true. Isotope patterns are signatures of chemical reactions, so they require additional context to be used as biosignatures. The framework of the Life Detection Knowledge Base discussed herein is used to convey arguments that support or challenge the utility of isotopic patterns for life detection. Examples of carbon and sulfur isotopic patterns in organic materials and minerals are presented to indicate how the life detection criteria "prevalence" and "signal strength" can be applied. In future work, more abiotic processes that might create false-positive life detection claims must be characterized. A broader range of microbial communities, taxa, and biomolecules should be explored for isotopic patterns. Additional elements also warrant investigation as potential isotopic biosignatures and environmental indicators. Studies of sedimentary macromolecular organic matter should be expanded further to provide deeper insights into isotopic abundance patterns.